2015-01-28T04:36:54ZThe Future of our Universe: From the 21st Century to the Endhttp://hdl.handle.net/2027.42/62071
The Future of our Universe: From the 21st Century to the End
Adams, Fred
This talk describes our current picture for the long term fate of the cosmos. We discuss the evolution of planets, stars, galaxies, and the universe itself over time scales that greatly exceed the current age of the universe. The story begins with the effects of accelerated cosmic expansion, which causes every galaxy cluster to become its own island universe in the ``near'' future. Next we discuss stellar evolution with a focus on the development of the most common, low mass stars. After accounting for the end of conventional star formation, we find the distribution of stellar remnants -- the neutron stars, white dwarfs, and brown dwarfs remaining after stellar evolution has run its course. In the resulting darkness, star formation continues at a highly attenuated rate through brown dwarf collisions. This process tapers off as the galaxy loses its stars, primarily by ejection through scattering encounters. As the galaxy disperses, weakly interacting dark matter particles are accreted by white dwarfs, where they annihilate and keep the old stellar remnants ``warm.” After the demise of the galaxy, the expelled degenerate objects (primarily white dwarfs) evaporate through the decay of their constituent nucleons. After these stellar remnants have disappeared, the black holes are the brightest astrophysical objects, slowly losing their mass as they emit Hawking radiation. After the largest black holes have evaporated, the universe slowly slides into darkness. Or does it?
2009-04-10T00:00:00ZBinary Pulsars and Relativistic Gravityhttp://hdl.handle.net/2027.42/62070
Binary Pulsars and Relativistic Gravity
Taylor, Joseph
Pulsars are neutron stars -- the extremely dense, strongly magnetized, rapidly spinning remnants of supernova explosions. They also appear to be nature's most precise clocks. Discovery of the first orbiting pulsar opened a new field of astrophysics in which the relativistic nature of gravity is tested through precise comparisons of "pulsar time" with atomic time here on Earth. Among other results, the experiments have demonstrated the existence of gravitational waves, as predicted by Einstein's theory of gravity.
2009-04-10T00:00:00ZUnveiling a Black Hole at the Center of Our Galaxyhttp://hdl.handle.net/2027.42/62069
Unveiling a Black Hole at the Center of Our Galaxy
Ghez, Andrea
More than a quarter century ago, it was suggested that galaxies such as our own Milky Way may harbor massive, though possibly dormant, central black holes. Definitive proof, for or against, the existence of a massive central black hole lies in the assessment of the distribution of matter in the center of the Galaxy. The motion of the stars in the vicinity of a black hole offers a way to determine this distribution. Based on 14 years of high resolution imaging, Dr. Ghez's team has moved the case for a supermassive black hole at the Galactic Center from a possibility to a certainty. Additionally, spectroscopy has revealed that the stars orbiting in such close proximity are apparently massive and young; the origin of these stars is difficult to explain, given the strong tidal forces, and may provide key insight into the growth of the central black hole.
2009-04-10T00:00:00ZA Revolution in Planetary Science: The Three-Zoned Solar Systemhttp://hdl.handle.net/2027.42/62068
A Revolution in Planetary Science: The Three-Zoned Solar System
Stern, Alan
Science’s view of our planetary system was fundamentally restructured by the 1990s discovery of the Kuiper Belt beyond Neptune and the recent discoveries of numerous Pluto-sized bodies in the Kuiper Belt. No longer do we view the solar system’s architecture as inner terrestrial planets and outer gas giants, with misfit Pluto orbiting beyond. Instead, Pluto is now seen in context, being one of many dwarf planets orbiting in a third zone, equally fundamental zone of our planetary system that lies beyond Neptune. I will describe this revolutionary transformation in astronomy’s worldview of our home solar system, as well as its implications for understanding both the taxonomy of solar systems around other stars and also for planet classification.
2009-04-10T00:00:00Z